It is well known to provide seepage resistant structures using water-swellable clays, such as bentonite, disposed across a path of possible seepage or flow. For example, this assignee's Bechtner U.S. Pat. No. 2,277,286 discloses the use of bentonite clay filled between spaced forms or bulkheads, such as wood, masonry or other suitable materials to hold the bentonite in place. Another of this assignee's prior patents to Arthur G. Clem, U.S. Pat. No. 3,186,896 discloses a moisture-impervious panel preformed from spaced paperboard sheets interconnected with an intermediate layer of a water-swellable clay, such as bentonite, that has been used for many years by this assignee as a waterproofing barrier. When subjected to leakage or seepage of water, the outwardly extending water-pervious paper or cardboard facing sheet will absorb the water and pass the water through the facing sheet contact with the intermediate layer of water-swellable clay thereby permitting the clay to hydrate, swell and block the passage of water completely through the panel.
One of the problems prevalent with the use of the moisture-impervious panels disclosed in the Clem U.S. Pat. No. 3,186,896 is that the paper or cardboard facing sheets sometimes are hydrated prior to complete installation, for example, when the panels are being installed and are wetted with rain water. Hydration prior to complete installation causes lateral movement of the swelled clay outwardly from between the facing sheets so that it is very difficult, if not impossible to fit two adjacent panels securely together without clay voids between adjacent panels. When adjacent panels are not fitted tightly together during installation, water first contacting the panels flows laterally over the facing sheets and finds a clay void space between adjacent panels so that water can penetrate between adjacent panels, at one or more of these clay void space locations before the intermediate water-swellable clay layer has had sufficient time to hydrate sufficiently and swell laterally to fill such clay void spaces Though such water damage will probably be of a relatively minor consequence, caused during a relatively short period of time until the intermediate water-swellable clay layer has had sufficient water contact for hydration, such water damage can be substantial and can create damage areas capable of substantial water penetration over time in addition to being very costly to excavate and repair. Although this problem has existed since the first use of these water-impervious panels, for over twenty years, presenting a long-felt need in this art, to date this problem has not been solved.
Many attempts have been made to improve upon the water-impermeability of multi-layer articles of manufacture containing bentonite. The following patents represent efforts to provide a water-impervious sheet material containing adhesively secured water-swellable clays: Clem U.S. Pat. No. 4,467,015; Clem U.S. Pat. No. 4,501,788; McGroarty et al U.S. Pat. No. 4,693,923; Harriett U.S. Pat. No. 4,656,062; and Harriet U.S. Pat. No. 4,787,780. Other patents disclose the use of water-impermeable layers for protecting a soil surface, such as British Patent specification No. 1,059,363; British Patent specification No. 1,029,513 and British Patent specification No. 1,129,840. Blias U.S. Pat. No. 4,344,722 discloses a water barrier constructed in the field by applying a first flexible, water-permeable fabric layer to a soil surface, overlaying a thickness of water-swellable clay material, and applying an overlayer of the same flexible, water-permeable fabric thereover. This eliminates the need for applying an adhesive to secure the clay to fabric sheets, but is expensive since the barrier material cannot be preformed but must be constructed in the field. U.K. published Pat. application GB 2,202,185A discloses a layer of water-swellable bentonite between flexible layers that have been needle punched together in a needle loom.
While many of the above-discribed prior art multi-layer, water-impermeable, bentonite-containing materials undoubtedly permit rapid hydration of the intermediate water-swellable clay layer, none of these patents have addressed the problem of preventing prehydration of bentonite panels by providing a water soluble coating material to a surface of the panel, for protection during installation.